The present invention relates to a binocular.
Generally, a binocular includes a mechanism such as a magnifying-power-varying mechanism and an operation knob for manually operating the mechanism. In case of a binocular with the magnifying-power-varying mechanism, two drive rings (for example, cam rings) are provided to left and right lens barrels for moving the lens groups. In order to transmit the rotation of the operation knob to the drive rings, the conventional binocular is provided with a gear train connecting the operation knob and the drive rings.
However, if the binocular further has an interpupillary adjustment mechanism (in which the lens barrels are swung about certain swing axes), the relative rotational position of adjacent gears of the gear train may be changed by the swinging of the lens barrels. If the relative rotational position of the adjacent gears changes, the drive rings are intentionally rotated. Thus, when the interpupillary adjustment is performed, the magnifying-power may be unintentionally varied.